Mass storage devices in personal computers and servers typically use rotatable media-based hard disk drives (HDDs), featuring one or more magnetic platters as the data carrier and a read/write head positioned over the relevant sector by means of an actuator. In recent years, the trend has been to miniaturize these HDDs such that currently the largest form factor is the 3.5 inch (about 8.9 cm) drive. The 3.5 inch drive is still the predominant device in desktop computers where they are typically mounted in drive bays. In the notebook sector, 2.5 inch (about 6.35 cm) drives are more commonly used in a slim form factor mounted in a specialized compartment in the chassis. With respect to the mounting considerations for the drive, aside from the actual physical dimensions, the weight of the HDD plays an important factor, in that certain prerequisites for the fixture have to be met. Moreover there are also some orientational factors that have to be taken into consideration, for example, drives mounted at an angle appear to have higher wear on their bearings than drives that lie flat with the spindle axis in a vertical orientation. Last but not least, the actuator movements entail enough mass displacement to cause some movements of the entire drive. Primarily because of the weight and stability concerns outlined above, hard disk drives are generally mounted in specialized drive bays within the chassis, often using rubber grommets to dampen vibrations and shock. Power and data connections are done through cabling to the motherboard or any add-on host-bus controller as well as the power supply unit.
The recent introduction of solid state drives (SSDs) into the market has eliminated some of the above concerns. An example of a conventional SSD 10 is schematically represented in FIG. 1 as comprising a printed circuit board 12 equipped with a power and data connector 14, multiple memory chips 16 and a control logic (controller) integrated circuit (IC) chip 18. The memory chips 16 typically comprise flash (e.g., NAND) non-volatile memory chips or another non-volatile memory technology. The connector 14 is shown as a male SATA connector that faces outward and away from the interior of the circuit board 12 to enable the SSD 10 to be connected to a cable of a computer system (not shown). SSDs of the type shown in FIG. 1 can be slimmer and lighter than conventional HDDs, and lack moving parts so that they do not vibrate during operation and have almost unlimited shock resistance. Likewise, they are not sensitive to any orientation whatsoever. However, a major drawback of current SSDs is their limited capacity compared to rotatable media. Even though there is a significant cost overhead for SSDs compared to HDDs, there is a market for large capacity SSDs. However, the current generation of controllers is not capable of addressing NAND memory space equivalent to the capacity of HDDs. Future generations of SSDs will be able to address higher densities of NAND flash, however, at the same time, capacity of HDDs will also have increased, resulting in a paradigm shift only without solving the problem of lag in storage capacity from SSDs to HDDs.
Redundant arrays of independent drives (RAID) configurations, including Spanning over several volumes in a “just a bunch of drives” (JBOD) configuration have been in the market for decades. These configurations are generally enabled using dedicated RAID cards with an ISA, PCI or PCI express (PCIe) interface. However, in this case, the system integrator still faces the issue of dedicated cabling and mounting hardware for each of the drives used in the array. Commonly-assigned U.S. patent application Ser. No. 12/713,349 to Schuette, whose contents are incorporated herein by reference, discloses such a system using a direct-mounting scheme of SSDs on a carrier board.
An emerging issue with striped RAID using SSDs is that the data transfer rates of the latest drives are reaching saturation of the host bus adapters and, in the case of high-end drives, easily saturate the logic interconnect of the entire computer system. In so far, it is not absolutely necessary to focus on raw bandwidth, as a single SATA (Serial Advanced Technology Attachment) interface may suffice. In addition, particularly the enterprise market is using precisely defined form factors for all components, and custom designs often cannot be implemented. A desirable solution would therefore be an implementation of several drives within an industry-standard HDD enclosure to warrant optimal compatibility with any existing system infrastructure.